1. Technical Field
The present invention relates to a solid-state image pickup device for converting incident light into electrical signals and to a manufacturing method thereof.
2. Related Art
In medical image diagnosis or non-destructive inspection, imaging is performed using radioactive rays such as X rays. However, since a reduction optical system is difficult to implement in imaging of the radioactive rays, the imaging is necessarily performed at the same magnification. Therefore, the medical image diagnosis or the non-destructive inspection requires a large imaging surface, and thus, a solid-state image pickup device having a variety of type of thin films deposited on a glass substrate or the like so that a plurality of pixels is arranged in a matrix form is used. Even when a 2-dimensional image sensor is configured by a solid-state image pickup device, since the image sensor requires a large imaging surface, a variety of type of thin films are deposited on a glass substrate or the like so that a plurality of pixels is arranged in a matrix form.
In such a solid-state image pickup device, each of the plurality of pixels includes a photoelectric conversion element capable of generating electric charges corresponding to an incident light intensity and a field-effect transistor having a drain thereof being electrically connected to a first electrode of the photoelectric conversion element. The gate and the source of the field-effect transistor are electrically connected to a gate line and a source line, respectively, and a bias line is electrically connected to a second electrode of the photoelectric conversion element. The solid-state image pickup device has a structure in which the field-effect transistor, the photoelectric conversion element, an insulating film and the bias line are formed in this order from a lower side of a substrate toward an upper side thereof. Therefore, when the solid-state image pickup device is formed, it is necessary to electrically connect the first electrode of the photoelectric conversion element to the drain of the field-effect transistor and to electrically connect the second electrode of the photoelectric conversion element to the bias line while forming the respective layers on the substrate in order.
As a connection structure for electrically connecting the first electrode of the photoelectric conversion element to the drain of the field-effect transistor, there is proposed a structure in which contact holes are formed in an insulating film on the substrate covering the photoelectric conversion element and the field-effect transistor so as to be disposed at a position where it overlaps with the second electrode of the photoelectric conversion element and a position where it overlaps with the drain electrode of the field-effect transistor, and in which connection wirings formed on the insulating film are electrically connected to the second electrode of the photoelectric conversion element and the drain electrode of the field-effect transistor via the contact holes (reference should be made to, for example, JP-B-3144091).
As a connection structure for electrically connecting the second electrode of the photoelectric conversion element to the bias line, there is proposed a structure in which the bias line is formed on an upper layer of the photoelectric conversion element, and a polyimide film is provided as an insulating material between the upper layer of the transistor and the photoelectric conversion element (reference should be made to, for example, JP-B-3050402).
However, when the structure disclosed in JP-B-3144091 is employed in electrically connecting the photoelectric conversion element and the field-effect transistor, it is necessary to form a number of contact holes on an upper layer side of the photoelectric conversion element. Therefore, there is a problem that the forming region of the photoelectric conversion element is reduced, and thus, the sensitivity decreases.
Moreover, when the structure disclosed in JP-B-3050402 is employed in electrically connecting the second electrode of the photoelectric conversion element and the bias line, the polyimide film may come into contact with a side surface of the photoelectric conversion element. Therefore, there is a problem that the semiconductor layer deteriorates with moisture contained in the polyimide film which is an organic film, and thus, the photoelectric conversion element deteriorates.